Cornea Confocal Microscopy: Utilities and Perspectives

The cornea is the ocular refractive medium with the greatest refractive power of the eye. The study of it is of vital importance for the diagnosis and follow-up of ophthalmological diseases with the aim of achieving high standards of visual acuity in our patients. Confocal microscopy of the cornea allows in-depth study of it, quickly, safely, painlessly, obtaining high-resolution images of the corneal sublayers. This chapter summarizes the procedure for performing corneal confocal microscopy, the normal characteristics of the tissue with real images of our patients, as well as a brief explanation of the main applications of this technology in the study of corneal dystrophies (keratoconus), in refractive surgery, corneal transplantation, infectious keratitis, glaucoma filtration bulla, among other topics.

Electromagnetic stress at the boundary: Photon pressure or tension?

It is well known that incident photons carrying momentum ℏkexert a positive photon pressure. But if light is impinging from a negative refractive medium in which ℏkis directed toward the source of radiation, should light exert a photon “tension” instead of a photon pressure? Using an ab initio method that takes the underlying microstructure of a material into account, we find that when an electromagnetic wave propagates from one material into another, the electromagnetic stress at the boundary is, in fact, indeterminate if only the macroscopic parameters are specified. Light can either pull or push the boundary, depending not only on the macroscopic parameters but also on the microscopic lattice structure of the polarizable units that constitute the medium. Within the context of an effective-medium approach, the lattice effect is attributed to electrostriction and magnetostriction, which can be accounted for by the Helmholtz stress tensor if we use the macroscopic fields to calculate the boundary optical stress.

Dispersion Characteristic of the Symmetric Slab Waveguide with Chiral Negative Refractive Medium

According to Maxwell equations and constitutive relations in chiral medium, the dispersion characteristic of the symmetric slab waveguide with chiral negative refractive medium is studied. The dispersion equations expressed in the normalized parameter are deduced in the slab waveguide. The numerical results show that the chiral parameter has great influence on the dispersion characteristic of slab waveguide. When the relative chiral parameter is about 0.0477, the zero order mode of left-handed polarized wave disappears. While it is greater than 1, the core becomes chiral negative refractive medium and the zero order mode disappears. In addition, compared with the general chiral waveguide, the tendency of dispersion curves in slab waveguide with chiral negative refractive medium is also analyzed.